1. Field of the Invention
This invention relates to a system of providing map data accumulated in a server through a computer network to a user terminal for the display of a map image, and a method of displaying the map image.
The present application claims priority from Japanese Application No. 2001-255159, the disclosure of which is incorporated herein by reference for all purposes.
2. Description of the Related Art
Information providing services of providing various types of information through a computer network such as the Internet include a map-information providing service for providing map data accumulated in a server through the computer network to a user terminal connected to the computer network as required, to allow the user terminal to display a desired map image.
FIG. 6 illustrates an example of map images displayed on the user terminal on the basis of map data provided by the map-information providing service as described above.
As shown in FIG. 6, in order to display a map image M within a map-image display frame F of a Web page for providing various types of map information, e.g., route retrieval and public-building retrieval for a navigation system, map data corresponding to the map image to be displayed must be downloaded from a map database site connected through the computer network to the user terminal in accordance with a request from the user terminal.
Conventionally, the map data for displaying the map image M in the web page is accumulated in a database in the map database site in such a way of forming a single data file for each map image displayed within the map-image display frame F. Upon a request from the user terminal, one of the data files corresponding to the request is read out from the map data files accumulated in the database, and transmitted to the user terminal to provide a display of the map image within the map-image display frame F in the web page displayed on the user terminal.
In this way, the user can display a desired map image in the web page by performing required operations, e.g. the inputting into the user terminal of a keyword for specifying an area of map to be displayed such as a place name, address, public-building name and the like.
However, in such a conventional system of displaying a map image as described above, for displaying a new map image besides the map image displayed in the map-image display frame F in the web page, the new map image has to be generated from a data file differing from the data file that includes the previous map image.
Accordingly, the data file including the new map image to be displayed is downloaded from the map database site, and the map-image display processing is performed once again from the beginning on the basis of the downloaded data file.
For this reason, even if the map image of an area required to be displayed is directly adjacent to an area of the displayed map image, for example, in the case of a web page configured to permit a display selecting operation for moving the center point of the existing map image on the screen so as to show an area adjacent thereto, when the display selecting operation is performed, the conventional system of displaying map images as described above newly performs the display processing for a map image corresponding to the area adjacent to the existing map image on the basis of another map data file. Hence, the conventional system has the problem of the impossibility of smoothly changing map images because of the long time lag until a new map image is displayed.
Further, for the reason that a map image displayed in a map-image display frame F in a web page is generated from an individual map data file, the user has problems associated with the use of map images, e.g., he/she will need time and effort for checking the continuity between the already displayed map image and the newly displayed map image, and may lose sight of a target position on the map image.